Because the quantity of local anesthetic crossing the placenta after maternal administration cannot be estimated by blood concentrations alone, we are evaluating the uptake and distribution of amide local anesthetics in chronically instrumented fetal lambs. The umbilical venous and the umbilical arterial concentration difference is evaluated by blood samples from the umbilical vein (UV) and fetal abdominal aorta (FA). Umbilical blood flow is measured by an electromagnetic flow probe implanted on the common umbilical artery (Qumb). (UV - FA) times Qumb equals fetal uptake. The accumulated uptake is calculated for the five hour observation period. Fetal urine excretion is measured at hourly intervals from a catheter placed into the bladder via the urachus. The total uptake is determined for each of the vital organs (brain, heart, liver, lungs, and kidneys). All local anesthetic concentrations are measured by high pressure liquid chromotography. Because local anesthetics possess varying physiochemical properties, we are studying lidocaine, mepivacaine, bupivacaine, etidocaine and prilocaine to relate the blood concentrations and uptake to these properties.